 To pass with flying colours means to have success at a difficult task, and it's a sailing term that dates back to the early 1700s. A ship's flag or banner was known as its colours, and when a ship or fleet was successful in battle and was returning to its homeland, it would sail in with its flag flying high on the mast. This indicated that the ship had been victorious. It had retained its flag rather than lost it to the enemy. To pass with flying colours was a sure sign of victory.